MICROGRAVITY EXPERIMENTS TO CHARACTERIZE ASTEROIDS’ BUILDING BLOCKS AT THE ZARM DROP TOWER IN BREMEN

GEMS (Granular Experiment in Microgravity with asteroid Simulant) is a microgravity experimental campaign carried out in the context of TRACES (Transitions in Rubble-pile Asteroid Chaotic Environment and granular Structures), an ERC-funded project led by Prof. Fabio Ferrari at the Department of Aerospace Science and Technology (DAER), Politecnico di Milano. GEMS Team includes DAER researchers Samuele Vaghi, Alessia Cremasco, Luigi Delfanti and Iosto Fodde. TRACES aims to uncover the properties and dynamical evolution of granular materials in asteroid environments, by developing new analytical and numerical tools, validated against experiments in a relevant environment.

The GEMS experimental campaign is funded by ESA and consists of 16 tests at the ZARM facilities in Bremen. The first half of the experimental campaign took place between October and November 2024. The experiment focused on observing collisions between asteroid simulant cobbles under microgravity and vacuum conditions, essential for replicating the asteroid environment. The simulant particles were carefully selected to closely match asteroid materials in terms of mechanical and surface properties.

The experimental setup was mounted inside a vacuum chamber that was dropped from the top of the 120-meter-high ZARM Drop Tower achieving approximately 4.7 seconds of free fall under microgravity conditions (10−6 g), among the best microgravity quality available worldwide. The trajectory of each cobble before, during, and after the contact was reconstructed using cameras. Two high-resolution, high-speed cameras, provided by the ZARM facility, were placed outside the vacuum chamber, while two GoPros (capable of withstanding decelerations of up to 50 g at the end of the drop) were positioned inside. Markers on the cobbles facilitated precise tracking. The collected data will now be analyzed and compared with numerical simulations. The second half of the experimental campaign is currently scheduled for March 2025.

TRACES aims at revealing the mechanical properties of asteroid constituents, primitive objects that have remained largely unchanged since the early Solar System. This holds a great potential both for asteroid science and space exploration, enabling new lander and rover investigations, resource utilization in space, and effective strategies for planetary defence, all while addressing one of the greatest challenges in physics: understanding the fundamental laws of granular materials.